Drill bit with pressure relief valve



Feb. 22, 1966 M. A. BROWN Filed June 20, 1963 I t \g FIG. 1

FIG. 2

MORRIS A. BROWN INVENTOR.

BY WiWM ATTORNEY United States Patent C) i 3,236,319 DRILL BIT WITH PRESSURE RELIEF VALVE Morris A. Brown, Dallas, Tex., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Filed June 20, 1963, Ser. No. 289,225 6 Claims. (Ci. 175-243) This invention relates to means for minimizing local pressure fluctuations below a drill bit within a liquidfilled borehole when raising and lowering the drill string. More specifically, this invention relates to an improved form of jet type drill bit which will relieve local pressure fluctuations below the bit as it is run in and out of a liquid-filled borehole.

In the drilling of boreholes with rotary, jet type hits, the phenomenon of downhole pressure fluctuations is the source of many difficulties. Since most liquids which are employed in the drilling of wells are gel-like and exhibit the property of thixotropy, such liquids resist a tendency to flow through the small nozzles of jet type bits to relieve local pressure fluctuations which may develop within a liquid-filled borehole below the bit as the bit is moved through the borehole. As a jet type bit is lowered into a liquid-filled borehole, the liquid below the bit must be displaced both around the bit and through the small jet nozzles in the bit. Generally, the passages through the bit and the space around the bit between the bit and the wall of the borehole are so small that high pressure surges are developed within the borehole ahead of the bit. Such high pressure surges may permanently damage oil-bearing formation-s penetrated by the borehole, preventing maximum production rates after the well is completed. The same restrictions to fluid flow both around the bit and through the bit may cause damaging pressure reductions within the borehole below the bit as the bit is pulled from the borehole. Pressure drops ranging from 300 to 400 pounds per square inch have been reported to have been caused by withdrawal of a bit from a borehole. In many instances, well blowouts have been attributed to a pressure drop at the bottom of a borehole caused by pulling the drill string out of the borehole. Pressure reductions in boreholes also often result in inward collapse of the wall of the borehole and in other destructive effects, such as shale slippage, which aggravate the problems of drilling.

Some work has been done in an attempt to alleviate pressure fluctuations below a bit within a borehole. Such work has generally involved the positioning of a relief valve within the drill string behind the drill bit. One of the most effective mechanisms thus far developed has been a check valve in the side of a drill collar which allows a pressure surge on the outside of the drill stem to be transmitted to the inside when going into the borehole. This mechanism does not, however, prevent pressure reductions when raising the drill string out of the borehole nor is it effective to prevent pressure surges when running the drill string into a borehole at a time when the bit has become balled. Under these latter conditions, the bit acts as a piston which creates high pressures in advance of it.

It is one object of the present invention to provide a mechanism for relieving pressure fluctuations within a liquid-filled borehole below a drill bit being introduced into or removed from the borehole. It is another object of the invention to provide a drill bit which has means for relieving pressure fluctuations below it as it is introduced into or removed from a liquid-filled borehole. It is a further object of the invention to provide a drill bit which is equipped with passage and valve means for relieving pressure increases as the bit is lowered into a liquid-filled borehole. It is a still further object of the ice invention to provide a drill bit having passage and valve means adapted to prevent pressure decreases as the bit is removed from a liquid-filled borehole.

In accordance with the invention, a conventional form of jet type drill bit is provided with an improvement which includes auxiliary or bypass fluid flow means having valve means therein for augmenting the drilling fluid capacity of the bit above the capacity of the jet nozzles at times other than when the bit is being used for jet type drilling. The valve means is adjusted to remain in an open position at all times except when a high jet velocity is desirable for drilling, thus allowing a large drilling fluid flow through the bit at times when the bit is being introduced into and removed from the borehole.

In the drawings:

FIGURE 1 is a longitudinal view in cross section illustrating a preferred form of drill bit constructed in accordance with the invention.

FIGURE 2 is a partial cross-sectional view of an alternative embodiment of the drill bit illustrated in FIG URE 1.

Referring to FIGURE 1 of the drawings, the reference numeral 9 denotes the lower end of a section of drill collar which functions to connect the drill bit to the drill string, not shown, and to provide supplemental weight to the drill bit. Connected to the lower end of drill collar 9 is a drill bit generally designated 10 which is constructed in accordance with a preferred embodiment of the invention. Drill bit ltl includes a body portion 11 to which is secured a plurality of cutting elements 12 which, as illustrated, are frusto conical in shape, though cutting elements of other shapes may be used. The body portion of drill bit It) comprises a shank 13, a central body portion 14, and a plurality of legs 15. Shank 13 is tapered and threaded to provide a convenient means of connecting the drill bit to the drill collar. Generally there is a leg 15 provided for each of the cutters 12, the number in general practice ranging from two to four depending upon the particular design of the drill bit. Extending through the shank 13 is a shank bore 2b which connects with a plurality of jet passages 21 in central body portion 14. Each of passages 21 extends through the central body portion, opening through the lower end of the bit in the vicinity of one of the cutting elements 12. Secured within each of passages 21 at the point where the passages open through the bottom of the bit is a jet nozzle element 22 which serves to direct the fluid flowing through passage 21 to the desired location. Passages 21 and nozzles 22 serve their primary function during drilling by conveying drilling fluid to the most effective location for washing cuttings from the vicinity of the drilling elements 12. Since the nozzles accelerate the drilling fluid flow to a velocity sufficient to effectively remove the cuttings, there is a restriction in the flow of drilling fluid through the drill bit through these passages and nozzles which is detrimental in other phases of a drilling operation in the absence of the improvement provided by the present invention.

In accordance with the invention, central body portion 14 is provided with an auxiliary or bypass fluid flow path 30 which, in the particular embodiment illustrated in FIGURE 1, is a central fluid flow passage extending through the drill bit body to provide fluid communication from shank bore 20 through the bottom of the drill bit. Fluid flow passage 30 serves to augment the normal fluid flow capacity of the drill bit to reduce pressure fluctuations below the bit in liquid-filled boreholes. F'l-ow passage 30 is permitted to function at those times other than during actual drilling when a pressure fluctuation below the bit may cause formation damage. Secured within passage 30 is a valve seat 31 which cooperates with ball valve 32 to control flow through passage 30.

Ball valve 32 is loaded by and supported on resilient means, such as a coil spring 33, which functions to keep the ball valve off of seat 31 at all times except when a force in excess of a predetermined amount is exerted on ball valve 32 by virtue of a pressure differential exerted across the ball valve. Ball valve 32 and its associated spring 33 are encased within and protected by a shroud element 34 which is open at its upper end and is provided with a plurality of ports 35. Shroud element 34 is tapered inwardly at its upper end, as illustrated, to prevent displacement of the ball valve from within the shroud element. Ports 35, the opening in the upper end of shroud element 34, the diameter of ball element 32, and spring 33 are so sized that when a predetermined fluid pressure is developed with-in the bit by a drilling fluid pump to circulate drilling fluid, ball valve 32 will seat upon seat 31 to force all of the drilling fluid through the jet nozzles. At all other times, ball valve 32 remains off seat 31 to allow drilling fluid to flow through passage 30.

The operation of the drill bit of FIGURE 1 will be described in terms of its function in a normal drilling operation to relieve pressure fluctuations below the drill bit which are likely to damage the formation being drilled. A spring 33 is chosen having a compressive strength of a value such that the spring will maintain ball valve 32 off seat 31 at all times except when drilling fluid is being pumped through the drill bit from surface pumps during the time that the drill bit is actually drilling and jetting action is desired. An example of a practical design of a drill bit in accordance with the invention to satisfy normal drilling conditions would be where the drilling fluid pressure within the drill bit during drilling is approximately 2000 pounds per square inch and the spring 33 employed has the capacity to maintain valve 32 off seat 31 at pressures up to 1500 pounds per square inch. As the drill bit is being lowered into a liquid-filled borehole, the action of spring 33 maintains ball valve 32 in an open position so that the drilling fluid in the borehole may freely flow not only through nozzles 22 and passages 21 into the drill string, but also through passage 30 into the drill string. Because of this large capacity of drilling fluid which is allowed to flow into the drill string, pressure build-ups within the drilling fluid in the borehole in advance of the drill bit are minimized if not entirely eliminated. Any balling around the bit caused by the contact of cutting elements 12 with the side of the borehole does not result in the drill bit acting as a piston. The fluid within the borehole flows upwardly through passage 30 and into the interior of the bit through ports 35 and shroud 34; and, if ball valve 32 is designed of such a size that there is space between it and the interior of the shroud 34, some of the fluid may flow into the bit around the ball valve through the shroud.

When the drill bit arrives at the point in the borehole that the drilling is to commence, a flow of drilling fluid through the drill string and drill bit will be initiated by surface-located pumps, resulting in :suflicient pressure being exerted above ball valve 32 to cause the ball valve to be lowered against the compression of the spring into contact with seat 31 effecting closure of passage 39. With passage 30 closed, all drilling fluid is forced to flow through jet passages 21 and nozzles 22 so that the drilling fluid will perform its conventional functions in connection with the drilling which includes jetting action against the bottom of the formation being drilled to cause removal of the chips cut from the formation by elements 12.

When it is desired that the drill string and drill bit be removed from the borehole, the surface pumps are stopped and flow of drilling fluid through the drill bit into contact with the formation is terminated with the borehole being left filled with drilling fluid. With the conventional form of drill bit, removal of the bit at this point often results in severe sudden pressure reductions below the drill bit. nowever, when a bit constructed in accordance with the invention is employed, upon termination of flow of the drilling fluid through the drill bit, spring 33 will force ball valve 32 from seat 31 to effect opening of the passage 30. As the drill bit is lifted from the borehole, the fluid within the drill collar and drill string freely flows back into the borehole, thus preventing severe pressure reductions below the drill bit within the borehole. Spring 33 has a compression strength which permits it to hold valve 32 in an open position at all times except when drilling fluid is being circulated through the bit at the pressure required for jetting action from the pumps. Thus, the draining of the drilling fluid from the drill string through the drill bit during removal of the drill bit from the borehole does not result in the closing of valve 32. The drilling fluid flows through shank bore 20 into passage 30 through ports 35 and from there through the bottom of the drill hit back into the borehole.

An alternative embodiment of the invention is illustrated in FIGURE 2 which shows a modified form of valve and bypass assembly which may be employed in a drill bit of the type shown in FIGURE 1. Referring specifically to FIGURE 2, fluid flow passage 30 includes two or more branch passageways 40 which extend through the central body portion 14 of the drill bit opening through the bottom of the drill bit in substantially the same manner as passage 30, as illustrated in FIGURE 1. A poppet type valve 41 supported on a valve stem 42 is slidably secured within passage 30. The upper end of passage 30 is shaped in the form of a valve seat 43 which cooperates with poppet valve 41 to effect the closure of the passage 30 to prevent the flow of any fluid through the passage. A spring 44 is positioned around the valve stem to maintain valve 41 in an open position at all times except when surface pumps are forcing drilling fluid through the drill bit into contact with the formation through the jet nozzles 22. The valve assembly and passageway means illustrated in FIGURE 2 function in a manner identical to that of the assembly shown in FIG- URE 1. This alternative form of valve and passageway means is shown only to illustrate that there are other ways of designing the apparatus contemplated by the invention, and thus it is not intended that the supplemental or bypass fluid passages within the drill bit and the associated valve means utilized therewith be limited to the specific designs illustrated. It is thus intended that the form of passage through the drill bit and the associated valve means enrployed therewith be limited only within the scope of the appended claims. It is also intended that the form of jet bit employed in the invention be not limited to the specific design illustrated. Most any bit having a body portion provided with jet passages and nozzles and cutting means secured to the body portion may be adapted to the invention.

What is claimed is:

1. In a jet-type drill bit adapted for use in the lower end of a liquid-filled borehole, said drill bit including an upper shank and a lower body portion, said shank being adapted to be connected to a drill string extending substantially to the surface, a bore extending through said shank to operatively connect a drill string to said body portion for fluid flow, cutting means secured to the lower end of said body portion and jet nozzles in said body portion to direct fluid flow adjacent said cutting means, jet passages extending through said body portion and interconnecting said shank bore with said jet nozzles to permit fluid flow between said shank bore and the bottom of said borehole, the improvement in said drill bit which comprises:

(a) at least one longitudinal bypass fluid flow passage within said body for interconnecting said shank bore with the said bottom of said borehole independently of said jet passages to minimize pressure drops through said drill bit when introducing said drill bit into, and removing said drill bit from, said liquidfilled borehole;

(b) a valve means secured within said bypass fluid flow passage to allow complete closure of said bypass fluid flow passage; and

(c) means biasing said valve into an open position at all times except when a drilling fluid is being circulated at jetting pressure through said drill bit from a drill string.

2. Apparatus in accordance with claim 1 wherein said bypass fluid flow passage extends substantially centrally through said drill bit body portion.

3. Apparatus in accordance with claim 1 wherein said valve means comprises a ball-type valve and said valve biasing means comprises a spring, said ball-type valve being supported on said spring, said spring having sufiicient compressive strength to maintain said valve in an open position at all times other than when drilling fluid is being circulated at jetting pressure through said drill bit from a drill string.

4. Apparatus in accordance with claim 3 wherein there is a valve seat positioned within said bypass passage, said ball-type valve being positioned above said valve seat, supported by said spring and cooperating with the valve seat to close said bypass passage; a shroud element secured within said drill bit around said valve seat and extending upwardly above said ball valve, said shroud element having an opening in the upper end thereof smaller than the diameter of said ball valve to prevent said ball valve from passing therethrough and port means through the side thereof below said ball valve when said ball valve is in said open position.

5. Apparatus in accordance with claim 1 wherein said valve means comprises a poppet-type valve and said valve biasing means comprises a spring, said poppet valve being supported on said spring, said spring having suflicient compressive strength to maintain said valve in an open position at all times other than when drilling fluid is being circulated at jetting pressure through said drill bit from a drill string.

6. Apparatus in accordance with claim 5 wherein said valve means comprises a valve seat including an upwardly facing, downwardly and inwardly tapering surface at the upper end of said bypass fluid flow passage, said valve having a stem positioned within said bypass fluid flow passage, means on said valve stem for retaining said valve stem within said bypass fluid flow passage, said poppet valve having a head at the upper end of said valve stem with a downwardly facing and inwardly and downwardly sloping surface to engage said valve seat to prevent a fluid flow through said bypass fluid flow passage, said valve biasing spring being a coil spring positioned around said valve stem and engaged between said poppet valve and said body portion to urge said poppet valve open, in an upward direction, away from said valve seat.

References Cited by the Examiner UNITED STATES PATENTS 2,944,794 7/1960 Myers -317 2,945,678 7/1960 Boudreaux et al. 175-317 CHARLES E. OCONNELL, Primary Examiner.

BENJAMIN BENDETT, Examiner. 

1. IN A JET-TYPE DRILL BIT ADAPTED FOR USE IN THE LOWER END OF A LIQUID-FILLED BOREHOLE, SAID DRILL BIT INCLUDING AN UPPER SHANK AND A LOWER BODY PORTION, SAID SHANK BEING ADAPTED TO BE CONNECTED TO A DRILL STRING EXTENDING SUBSTANTIALLY TO THE SURFACE, A BORE EXTENDING THROUGH SAID SHANK TO OPERATIVELY CONNECT A DRILL STRING TO SAID BODY PORTION FOR FLUID FLOW, CUTTING MEANS SECURED TO THE LOWER END OF SAID BODY PORTION AND JET NOZZLES IN SAID BODY PORTION TO DIRECT FLUID FLOW ADJACENT SAID CUTTING MEANS, JET PASSAGES EXTENDING THROUGH SAID BODY PORTION AND INTERCONNECTING SAID SHANK BORE WITH SAID JET NOZZLES TO PERMIT FLUID FLOW BETWEEN SAID SHANK BORE AND THE BOTTOM OF SAID HOREHOLE, THE IMPROVEMENT IN SAID DRILL BIT WHICH COMPRISES: (A) AT LEAST ONE LONGITUDINAL BYPASS FLUID FLOW PASSAGE WITHIN SAID BODY FOR INTERCONNECTING SAID SHANK BORE WITH THE SAID BOTTOM OF SAID BOREHOLE INDEPENDENTLY OF SAID JET PASSAGES TO MINIMIZE PRESSURE DROPS THROUGH SAID DRILL BIT WHEN INTRODUCING SAID DRILL BIT INTO, AND REMOVING SAID DRILL BIT FROM, SAID LIQUIDFILLED BOREHOLE; (B) A VALVE MEANS SECURED WITHIN SAID BYPASS FLUID FLOW PASSAGE TO ALLOW COMPLETE CLOSURE OF SAID BYPASS FLUID FLOW PASSAGE; AND (C) MEANS BIASING SAID VALVE INTO AN OPEN POSITION AT ALL TIMES EXCEPT WHEN A DRILLING FLUID IS BEING CIRCULATED AT JETTING PRESSURE THROUGH SAID DRILL BIT FROM A DRILL STRING. 